Double-walled chimneys are known in the art, one example of which is disclosed in the U.S. Pat. No. 3,902,744 to Stone and prior art cited therein. The basic construction involves inner and outer concentric pipes affording an annular insulating space between them. Fundamentally, the assembly or erection of the chimney proceeds with coaxial, end-to-end stacking of, say, a pair of inner pipes, the meeting ends of which are radially outwardly flanged to receive an inner annular ring which clamps the pipes together.
Another example of a double-walled chimney is disclosed in U.S. Pat. No. 4,724,750, which is incorporated by reference herein. These and other prior art references show that it is known in the art to fabricate corresponding flanges on two adjacent sections at the interface thereof. The flanges are typically transverse to the basic axis of the chimney section. Typically an annular ring is placed over the junction of the two corresponding flanges to better seal the chimney.
Although these flanged chimney sections are well known when the cross-sectional shape of the chimney is circular or angular (such as rectangular, square, etc.), the prior art does not disclose a flanged chimney section or corresponding connection system for chimneys with a cross-sectional area that is rounded but non-circular. One such rounded but non-circular shape is often referred to as “obround.” As used herein, “obround” is defined as a shape consisting of two semicircles connected by parallel lines tangent to their endpoints.